1. Field of the Invention
The present invention relates to an improved diesel fuel which contains a synergistic combination of additives comprised of a peroxidic cetane booster such as ditertiary butyl peroxide, together with an alkyl glycol ether having ##STR1## wherein R is an alkyl group, R.sub.1 is a C.sub.1 -C.sub.2 alkyl group, R.sub.2 is hydrogen or methyl, and n is an integer of 1 through 5, or a polyol where R is hydrogen, n is 4 to 30, and R.sub.1 and R.sub.2 are as above.
2. Description of the Prior Art
Diesel fuels are known which contain a synergistic cetane improving additive combination of a peroxidic component and an aliphatic polyether of the formula R(--O--X).sub.n O--R.sup.1 where R and R.sub.1 are alkyl groups, X is an alkylene group and n is an integer. See U.S. Pat. No. 2,655,440 and divisional U.S. Pat. No. 2,763,537.
European Application 80-100827.7 describes the use of various propylene glycol mono- an di-ethers as a component of diesel fuels. The compositions described in this reference involve a multicomponent formulation which includes polyethers, acetals, lower alkanols, water and up to 85 volume % diesel fuel hydrocarbons. The specific synergistic formulation of the present invention is not taught or described.
U.K. 1,246,853 describes the addition of dialkyl ethers of propylene glycol as smoke suppressants in diesel fuel.
U.S. Pat. No. 4,753,661 describes a fuel conditioner which comprises a polar oxygenated hydrocarbon which may be combined with a compatibilizing agent which is an alcohol and which may be tripropylene glycol monomethyl ether.
Japanese Published Application 59-232176 describes the use of the di-ethers of various polyoxyalkalene compounds as diesel fuel additives.
The Clean Air Act Amendments of 1990 have established certain emission standards for heavy duty diesel engines, in particular with regard to nitrogen oxide and particulate matter emissions. The contribution of diesel fuel sulfur content to exhaust particulates has been well established, and has led to an EPA regulation which will require highway diesel fuels to contain no more than 0.05 wt. % sulfur. In 1991, particulate matter emissions were required to drop from 0.60 to 0.25 grams/BHP-hr., and in 1994 the emission limit is 0.10. Similarly, nitrogen oxide will decrease from 6.0 to 5.0 in 1994 and from 5.0 to 4.0 grams/BHP-hr. in 1998. The California Air Resources Board (CARB) has issued regulations that are viewed as more difficult to meet than the EPA targets. To qualify a diesel fuel in California, emissions must be no greater than the CARB reference fuel which contains 0.05 wt. % maximum sulfur, 10% maximum aromatics and a minimum cetane number of 48.
Many strategies are being used by the industry to reduce emissions. Improved heavy duty diesel engine designs including higher injection pressures, turbocharging, air intercooling, retarded injection timing through electronic tuning control, exhaust gas recycle and exhaust aftertreatment devices all lower emissions. For this advanced technology to work, a high quality, low emissions diesel fuel is required in addition to the use of various fuel additive improvements including cetane improver use, diesel fuel detergents to keep fuel injectors clean and improved low ash engine oils. A combination of these strategies will be utilized to meet new clean air standards. The key issue is to find the most effective combination of technologies which offer the best cost/performance.
Fuel regulations, especially those promulgated in California, will require costly changes in diesel fuel composition. Desulfurization to achieve the 0.05 wt.% sulfur target is easily accomplished through mild hydrogenation. However, refiners must use deep hydrogenation to decrease aromatic content from the current 30-40% aromatic level down to 10%. Many refiners have elected to exit the California diesel fuel market rather than making the high capital investment required for deep hydrogenation. At least one refiner was able to qualify a diesel fuel for California by lowering the aromatics to 19% and increasing the cetane number from 43 for a typical fuel up to around 60 using an alkyl nitrate cetane improver.
The present invention relates to an additive combination of peroxide cetane improver and an alkyl glycol monoether or polyol which, when incorporated in standard 30-40% aromatic containing diesel fuel, provides reduced emissions of nitrogen oxides, particulate matter, hydrocarbons, carbon monoxide and unregulated aldehyde emissions, thus providing a fuel capable of meeting even the California standards. In addition, the use of the additive combination of the present invention provides a synergy whereby a significant increase in fuel economy is achieved.